Stress fixtures delivering 2.8 kg/cm2 will be applied to monkey intervertebral discs for 90-day intervals. In vivo measurements of intranuclear pressure will be made to determine the rate of pressure relaxation. Injections of S35 sulfate and H3 proline/lysine prior to sacrifice will be made to assess biosynthetic effects of the compression. Stressed disc will also be tested in compression/tension modes to assess alterations in material properties. Piezoelectric properties of stressed and control discs will be attempted to determine if the properties can be correlated with the degree of degeneration observed.